Sometimes, injection valves comprise a disc element, sometimes called “hydro-disc”, which is arranged in an axial region of the valve needle facing towards the fluid outlet portion and fixedly connected to the valve needle. The disc element limits the movement of the armature. Furthermore, it operates to dissipate kinetic energy of the armature during the closing-phase of the valve, because fluid is squeezed through the gap between the armature and the disc element. Thus, the disc element helps to reduce bouncing of the needle and post-injections.
A large diameter of the disc element causes the armature to start moving more slowly, when the coil of the electro-magnetic actuator unit is energized. Consequently, less kinetic energy may be accumulated before the actual opening, which reduces the maximum fuel pressure of the valve.
On the other hand, the armature moves towards the disc element after closing of the valve, generating a fluid flow in clearances between the armature and the upper retainer and disc element, generating an additional closing force for the valve. This additional closing force, which helps to reduce bounce and post-injections, is larger if the diameter of the disc element is larger.